Optically active dihydropyran derivatives represented by formula (1) are useful compounds, for example, as intermediates for syntheses of the saccharides described in A. KONOWAL et al., Tetrahedron, Vol. 32, pp. 2957-2959 (1976) or of the antibiotics described in K. C. Nicolaou et al., J. Org. Chem., pp. 1440 (1985) and STEVEN D. BURKE et al., Tetrahedron, Vol. 42, pp. 2787-2801 (1986).
Hitherto, as processes for producing such optically active dihydropyran derivatives of formula (1), a process in which 1-methoxy-1,3-butadiene or 1,3-pentadiene is reacted with a glyoxylic acid ester in the presence of a catalyst which is menthoxyaluminum dichloride or Eu(hfc).sub.3, i.e., europium (III) tris[3-heptafluoropropylhydroxymethylene)-(+)-camphorate] has been reported in M. Quimpere et al., J. Chem. Soc., Chem. Commun., pp. 676-677 (1987).
However, the above-described known process has the following drawbacks. The optically active site in each of the catalysts to be used in the process has a specific absolute configuration derived from a naturally occurring raw material, that is, absolute configurations for menthoxyaluminum dichloride and Eu(hfc).sub.3 are derived from (-)-menthol and (+)-camphor, respectively. However, even when products respectively having the absolute configurations corresponding to those of the two catalysts are intended to be obtained, the menthoxyaluminum dichloride catalyst cannot yield a desired product having an industrially utilizable optical purity. Hence, it has virtually been possible to produce only products having a specific absolute configuration obtained from the Eu(hfc).sub.3 catalyst derived from (+)-camphor. In addition, even with the Eu(hfc).sub.3 catalyst, attainable optical purities of the products are 64% ee at maximum, which value is attained with (2R,6S)-2-methoxy-6-methoxycarbonyldihydropyran. It has, therefore, been desired to develop a process for producing a dihydropyran derivative having an even higher optical purity.